Functional studies on two catalase genes from tomato (Solanum lycopersicum L.)

We investigated the expression profiles of two catalase genes (Slcat1 and Slcat2) in Solanum lycopersicum leaves in response to different treatments, including abiotic and oxidative stress. The Slcat1 and Slcat2 proteins had higher levels of identity with catalases from other solanaceous plants than between themselves. At least one copy of each of the Slcat1 and Slcat2 genes was present in the tomato genome. Expression of the Slcatl gene was high in stems and flowers, while expression of Slcat2 was high in leaves. Slcatl and Slcat2 gene expression were differentially regulated in a circadian rhythm. Slcatl gene expression was high late in the light phase and early in the dark phase of the day, while Slcat2 gene expression was high late in the dark phase and early in the light phase. Slcatl was highly transcribed after various stress treatments with salt (NaCl), dehydration, lead (Pb), hydrogen peroxide (H2O2), methyl viologen (MV), or abscisic acid (ABA). The levels of Slcatl mRNA increased between 4 - 24 h in stress-treated tomato leaves. Slcat2 mRNA accumulated to high levels in non-stressed control leaves and was responsive to light. Catalase activity was observed to increase in response to all these stress treatments. Our results suggest that Slcatl may be the major scavenger of H2O2 under adverse stress conditions, thereby maintaining homeostasis in the levels of reactive oxygen species and thus helping to mitigate the effects of environmental stress. Slcat2 may be involved in the breakdown of the H2O2 produced during photorespiration. In addition, the Slcat2 gene may respond to salinity stress in tomato.